A site that is 3 months old has likely had no time to build authority. Google will generally consider new sites with "suspicions". When I say this, I do not mean that Google will automatically never consider ranking new sites, but essentially you need to prove to Google that your site is worthy of ranking.

To do this you need to:

1) Produce unique content (things people want to read, the more interesting it is the more chance people will link to it)

2) After writing up some decent content you will want to build some backlinks... consider finding people who have author rights to certain blogs where they can write an article for you on the blog and link back to you.
Consider the following to acquire the most juice from these blogs
a) Blog that have authority
b) Blog has good / high volume of traffic
c) Blog is related to your niche (relevance)

Here I am asking you that your website's ranking disappears for almost all the keywords. If it is true then check webmaster tool is there any suggestions that Google is asking you to improve? If your website's ranking is fluctuating for the one or two, three keywords then nothing to be worried. It is common.